Immunohistochemical study of cytokeratin distribution in the collecting duct of the human kidney.

In order to assess the expression of different cytokeratins in the collecting duct cells (CDCs) of the human kidney, three consecutive sections were stained with periodic acid-Schiff, CAM 5.2 and AE-1 (CAM 5.2 recognizes cytokeratins #19,18,8 and AE-1 #19,16,15,14,10 of Moll's catalog.), respectively. By comparing these sections, it was found that most CDCs in the inner medulla were both CAM 5.2- and AE-1-positive, whereas in the outer medulla and cortex, 77% of the CDCs were both CAM 5.2- and AE-1-positive, 15% CAM 5.2-positive and AE-1-negative, 8% both CAM 5.2- and AE-1-negative, and 0.4% CAM 5.2-negative and AE-1-positive. Recent studies have shown that most CDCs express low-molecular-weight cytokeratins #7,8,18 and 19 (17, 18, 19, 20). Of these cytokeratins, CAM 5.2 recognizes cytokeratins #8,18,19 and AE-1 recognizes cytokeratin #19. Therefore, most CDCs belong to one of the following three major types; 1. Those positive for cytokeratins #8,18 and 19 (CAM 5.2- and AE-1-positive), 2. Those positive for cytokeratins #8 and 18 and negative for #19 (CAM 5.2-positive and AE-1-negative) and 3. Those negative for cytokeratins #8,18 and 19 (CAM 5.2- and AE-1-negative). A few CAM 5.2-negative and AE-1-positive cells were thought to express high-molecular-weight cytokeratins. The significance of these various cytokeratin expressions is discussed.